Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for determining the number of hybrid automatic repeat request (HARQ) processes in a wireless communication system in which serving cells using a radio frame of different types are aggregated.
Related Art
Long term evolution (LTE) based on 3rd Generation Partnership Project (3GPP) Technical Specification (TS) is one of mobile communication standards. Meanwhile, 3GPP LTA-advanced (LTE-A) which is an evolution of 3GPP LTE is currently underway. A technique introduced in 3GPP LTE-A is a carrier aggregation.
A carrier aggregation uses a plurality of component carriers. A component carrier is defined by the center frequency and a bandwidth. One downlink component carrier or a pair of an uplink component carrier and a downlink component carrier correspond to one cell. It can be said that a terminal being served using a plurality of downlink component carriers is being served from a plurality of serving cells.
Meanwhile, an error compensation technique, which is to secure the reliability of wireless communications, includes a forward error correction (FEC) scheme and automatic repeat request (ARQ) scheme. In the forward error correction (FEC) scheme, an error at a reception unit is corrected by adding extra error correction codes to information bits. The FEC scheme has an advantage in that there is less time delay and no information required to be transmitted and received between a transmission unit and a reception unit, however, it is a weak point that system efficiency is low in good channel conditions. The ARQ scheme is strong at transmission reliability, however, it causes time delay and the system efficiency is low in poor channel conditions.
The hybrid automatic repeat request (HARQ) is a scheme in which FEC and ARQ are coupled, it checks whether to include an error that data received by a physical layer cannot be decoded, and if the error is occurred, efficiency can be increased by requesting retransmission.
A receiver in HARQ, if an error is not detected in data received, informs a success of the reception by transmitting an acknowledgement signal to the reception acknowledgement. If an error is detected in data received, a receiver informs a transmitter of the error detected by transmitting a NACK signal to the reception acknowledgement. If the NACK signal is received, the transmitter may retransmit data.
Meanwhile, in the carrier aggregation in of the next generation wireless communication systems, serving cells using TDD and serving cells using FDD may be aggregated. That is, a plurality of serving cells that uses different types of radio frames may be allocated to a UE. In a conventional art, it is defined to aggregate the serving cells that use identical type of radio frames only in carrier aggregation. Accordingly, it is not considered of a method that determines the number of HARQ processes in aggregation of serving cells that use different types of radio frames.
In case that serving cells that use different types of radio frames are aggregated, it is problematic in which way the number of HARQ processes, which are simultaneously capable, is determined.